That was my first try of actually putting the storm into the texture and I also thought it was a little too big. But if you notice that Isabel is merging with the stormfront over the eastern US that is part of the original cloudmap. If I erased some of the original stormfront, Isabel would probally look smaller.
The reason that I used a 4k is because I think that is the size limit

Anyhow, the screenhots at the start of this thread show a seperate model with the storm. That model is actually 9 meshes. 8 for the planet and 1 for the storm. Each mesh can handle a 4k texture so all together the model can draw a 16k. What I did the first time was make the 9th mesh (katrina) too small. The texture for it can be 4k also. I made a larger mesh for it but could not get the clouds to match up (look right). A couple screenshots:




The last shot is basic rendering.
Thats when I tried to put the storm into the cloudlayer.By combinning the layers as you said, with the land, this will make things a little easier. The cloudmap I'm using as a base is the 8k version from the BMNG site. And if you look closely at it you can see the outline of Flordia in it. That's what I used as a guage. What I should do is create a earth texture with a grid on it that displays pixel count and blender units to use as a tool.
But I'm bound by the power's of 2 for my texture size of the storm that I place into the main cloud layer, also due to my older card, if I want to use it as a texture for a 9th mesh. That shot of Isabel is actually 256x256 in the 8k cloudmap. 128x128 is too small. I think I have to scale down the storm a little more and use a 256x256 of it.But I need border clouds to ease the transition from the storm to the base. Confused yet? So am I. I am finding it almost impossible to put into words what I am trying to do.
The base texture of Isabel I used from NASA/NOAA is 250m reoloution, about 5000x6000. Thats scaling down quite a bit.
cartrite